JP5270230B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In recent years, a fuel cell has attracted attention as a power source excellent in operating efficiency and environmental performance. A fuel cell generates power by an electrochemical reaction between a fuel gas and an oxidizing gas. The electrochemical reaction between the fuel gas and the oxidizing gas is performed in a fuel battery cell that supports a catalyst.

Water accompanying the electrochemical reaction between the fuel gas and the oxidizing gas is generated in the fuel cell. For example, Patent Document 1 discloses a technique for improving the power generation performance by adjusting the flow of reaction gas and cooling medium of a fuel cell to control the relative humidity in the reaction gas. Patent Document 2 discloses a technique for bypassing the supply of gas to a fuel cell when an abnormality occurs in some of the plurality of fuel cells. In addition, Patent Documents 3 to 5 disclose techniques for controlling the gas flow in the cell plane.
JP 2004-31135 A JP-A-10-255827 JP 2000-30730 A JP-A-5-94831 Japanese Patent Laid-Open No. 7-249419

  The electrochemical reaction between the fuel gas and the oxidizing gas is performed by protons moving from the fuel electrode side to the oxygen electrode side through the electrolyte membrane. Therefore, if the water on the fuel electrode side moves to the oxygen electrode side as the accompanying water of protons, or if the fuel cell enters an operation state with high output and low humidification, the water on the fuel electrode side becomes insufficient and the gas flow It becomes easy to dry the downstream side of the road. In the portion where the electrolyte membrane is dried, the movement of protons is inhibited by drying, so that the power generation is stopped and water accompanying the electrochemical reaction is not generated. If a portion where water is not generated is generated, the water flowing to the other portion disappears, so that the dried portion gradually expands, and there is a possibility that power generation will eventually be stopped. This invention is made | formed in view of the subject which concerns, and makes it a subject to provide the technique which suppresses the fall of the electric power generation of the whole fuel cell system by the power generation failure which arose in the fuel cell expanded.

  In order to solve the above problems, the present invention stops the supply of fuel gas and oxidizing gas to the fuel cell stack where the electrolyte membrane is dry.

Specifically, a fuel cell system that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas, the first fuel cell stack in which a membrane electrode assembly is bonded so that an electrolyte membrane is sandwiched between catalyst electrode membranes And the second fuel cell stacking section, and the first fuel cell stacking section and the second fuel cell in the first fuel cell stacking section and the second fuel cell stacking section. A fuel gas flow path that flows in the order of the stacking section, the fuel gas flow path passing through the catalyst electrode film on the fuel electrode side of the membrane electrode assembly of each fuel cell stacking section, the second fuel cell stacking section, and the An oxidizing gas flow path for flowing the oxidizing gas through the first fuel cell stacking section in the order of the second fuel cell stacking section and the first fuel cell stacking section, and a membrane electrode junction of each fuel cell stacking section An oxidizing gas passage passing through the catalyst electrode membrane on the oxygen electrode side of the body, and the fuel gas When the electrolyte membrane of the membrane electrode assembly of the second fuel cell stack is dry while the oxidizing gas flows through the fuel gas channel and the oxidizing gas flows through the oxidizing gas channel, the fuel gas flowing through the fuel gas channel And bypass means for bypassing the oxidizing gas flowing through the oxidizing gas flow path to the second fuel cell stack.

  The amount of water in the electrolyte membrane differs greatly between the upstream side and downstream side of the gas flow path, and the downstream side is unlikely to receive water supply on the fuel electrode side where moisture gradually decreases along the flow direction. On the oxygen electrode side where the water produced by the electrochemical reaction is generated, the upstream side is not easily supplied with water. Therefore, in the case of the counter channel system, the electrolyte membrane downstream of the fuel electrode is particularly easy to dry, and once a dry site is generated and a site where generated water is not generated is generated, movement of proton-associated water and heat generation due to current continue. Therefore, recovery to a wet state cannot be expected, and further, the drying site is easily expanded due to the stop of the supply of generated water to the downstream side of the oxygen electrode. Therefore, the fuel cell system is a case where there are two stacked portions in which membrane electrode assemblies are stacked, and the fuel gas flow path and the oxidizing gas flow path pass through each stacked section in order, and one of the fuel cell stacked layers One fuel cell stack when the section is downstream with respect to the direction of fuel gas flow and upstream with respect to the direction of flow of oxidizing gas with respect to the other fuel cell stack The part is bypassed as the electrolyte membrane dries. The one fuel cell stack portion is the second fuel cell stack portion referred to in the present invention, and may form a single stack or two or more stacks in appearance. It may be. That is, the second fuel cell stack is a stack on the downstream side of the fuel gas and the upstream side of the oxidizing gas when there are two fuel cell stacks. In addition, the other fuel cell stack portion is the first fuel cell stack portion referred to in the present invention, and may form a single stack or two or more stacks in appearance. You may do. That is, the first fuel cell stack is a stack on the upstream side of the fuel gas and the downstream side of the oxidizing gas when there are two fuel cell stacks. The first fuel cell stack and the second fuel cell stack may be combined to form a single stack in appearance. In this case, it is necessary to sandwich a member that enables electrical disconnection between the first fuel cell stack and the second fuel cell stack and also allows the gas flow to be blocked.

  When the electrolyte membrane of the second fuel cell stack is dry, the fuel cell system stops power generation in the stack. The stop of the power generation in the stacked portion is realized by bypassing the flow of the fuel gas and the oxidizing gas. This is because it is possible to suppress the progress of drying of the laminated portion that is normally generating electricity. When the flow of fuel gas and oxidant gas is bypassed, the accompanying water that has moved to the cathode side accompanying the movement of protons in the electrolyte membrane returns to the anode side, so recovery of the dry part to the wet state is expected. It is. Therefore, a decrease in the generated power of the entire fuel cell system due to the expanded portion where the electrolyte membrane is dried is suppressed.

  Further, in the fuel cell system, when the bypass means bypasses the second fuel cell stack, the areas of the first fuel cell stack and the whole membrane electrode assembly of the second fuel cell stack The flow rate of the fuel gas flowing through the fuel gas flow path and the oxidizing gas flowing through the oxidizing gas flow path by a predetermined ratio that is the ratio of the area of the membrane electrode assembly of the second fuel cell stacking portion occupied in It may further comprise a flow rate control means for reducing the flow rate.

  By bypassing the second fuel cell stack, the amount of fuel gas and oxidizing gas consumed by the entire first fuel cell stack and the second fuel cell stack is reduced. Since the amount of fuel gas and oxidizing gas consumed is proportional to the size of the reaction surface of the membrane electrode assembly through which the reaction gas flows, the fuel gas flow is reduced by the amount reduced by the bypass of the second fuel cell stack. The amount of gas flowing through the channel and the oxidizing gas channel may be reduced. This reduced amount is referred to as a predetermined ratio in the present invention, and is a ratio of the flow rate of gas that becomes unnecessary due to the bypass of the second fuel cell stack. By adjusting the gas flow rate according to the control of the gas flow path by the bypass means, the supply of unnecessary fuel gas and oxidant gas is suppressed to improve the operation efficiency of the entire system, and the power generation is normally performed. It is also possible to suppress the drying of the part.

  Further, when the electrolyte membrane of the membrane electrode assembly of the second fuel cell stack portion is wet with the bypass means bypassing the second fuel cell stack portion, the second fuel cell stack portion The fuel gas and the oxidizing gas may be allowed to flow through the fuel gas channel and the oxidizing gas channel. When the electrolyte membrane of the second fuel cell stack is wet, the supply of fuel gas and oxidizing gas to the stack is started, so that the power generation capability of the fuel cell system can be fully exhibited. In addition, the electrolyte membrane being wet means that the dried electrolyte membrane is wetted, so that a state in which power generation is possible when the fuel gas and the oxidizing gas are supplied.

  The bypass means may detect dryness of the electrolyte membrane of the membrane electrode assembly based on the conductivity of the membrane electrode assembly of the second fuel cell stack. Since water easily conducts electricity, the conductivity between both electrodes of the membrane electrode assembly that sandwiches the electrolyte membrane changes when the wetness of the electrolyte membrane changes. Therefore, by measuring this, it is possible to grasp the dryness of the electrolyte membrane.

  It is possible to provide a technique for suppressing a decrease in generated power due to expansion of a portion of power generation failure occurring in a fuel cell.

  Hereinafter, an embodiment of the present invention will be exemplarily described. Embodiment shown below is an illustration and this invention is not limited to these.

<Configuration of Embodiment>
FIG. 1 is a configuration diagram of a fuel cell system 1 according to the present embodiment. As shown in FIG. 1, the fuel cell system 1 includes a fuel cell stack 2A (corresponding to a second fuel cell stack portion in the present invention) and a fuel cell stack 2B (first fuel cell in the present invention). A hydrogen storage tank 3 for supplying hydrogen as a fuel gas to the anode side of the fuel cell stacks 2A and B, and air containing oxygen as an oxidizing gas on the cathode side of the fuel cell stacks 2A and B. A compressor 4 for supplying (corresponding to a part of the flow rate control means in the present invention) is provided. The fuel cell system 1 also includes an electronic control unit 5 (ECU: Electronic Control Unit) that controls each device. The fuel cell system 1 according to the present embodiment is mounted on a fuel cell vehicle that runs on an electric motor (load), and is premised on supplying electric power to an electric load such as an electric motor. However, the present invention is not limited to this, and the fuel cell system according to the present invention may be installed on the ground or mounted on a moving medium other than an automobile.

  The fuel cell stacks 2 </ b> A and 2 </ b> B are polymer electrolyte fuel cells (PEFC) suitable for a moving medium such as a fuel cell vehicle, and generate power by being supplied with hydrogen and oxygen. The fuel cell stacks 2A and 2B are equipped with many membrane electrode assemblies (MEA: Membrane Electrode Assembly) that generate electricity by an electrochemical reaction between hydrogen as a fuel gas and oxygen as an oxidant gas. Are stacked so that a desired voltage is output. In the present embodiment, it is assumed that the fuel cell stacks 2A and 2B have a counter flow channel system in which the cathode side (oxygen electrode side) gas and the anode side (fuel electrode side) gas flow in opposite directions. It is said.

  The fuel cell stacks 2 </ b> A and 2 </ b> B have substantially the same performance, and are arranged in series on the fuel gas channel 6 and the oxidizing gas channel 7. That is, the air flowing through the oxidizing gas passage 7 pressurized by the compressor 4 passes through the fuel cell stack 2B after passing through the fuel cell stack 2A, and the fuel gas passage exiting from the hydrogen storage tank 3 6 passes through the fuel cell stack 2A and then passes through the fuel cell stack 2A.

  The fuel cell system 1 includes a hydrogen inlet valve 8 (corresponding to a part of the flow control means in the present invention) in the middle of the fuel gas flow path 6 for supplying hydrogen from the hydrogen storage tank 3 to the anode side of the fuel cell stack 2B. Yes). The hydrogen inlet valve 8 is a control valve whose opening degree can be adjusted by a command from the electronic control unit 5 and controls the hydrogen flowing from the hydrogen storage tank 3 to the fuel cell stacks 2A and 2B.

  The fuel cell system 1 also includes a fuel gas bypass channel 9 for bypassing the hydrogen flowing through the fuel gas channel 6 to the fuel cell stack 2A. The upstream side of the fuel gas bypass passage 9 is connected to the fuel gas passage 6 connecting the fuel cell stack 2B and the fuel cell stack 2A via the bypass valve 10A-H, and the downstream side is connected via the bypass valve 10B-H. And connected to the fuel gas flow path 6 on the downstream side of the fuel cell stack 2A. The bypass valves 10A-H and 10B-H are electromagnetic three-way valves, and flow hydrogen flowing through the fuel gas flow path 6 to the fuel cell stack 2A side in response to a command from the electronic control unit 5, or a fuel gas bypass flow path. Or flow to the 9th side.

  In addition, the fuel cell system 1 includes a hydrogen outlet valve 11 in the middle of the fuel gas flow path 6 that discharges hydrogen off-gas from the anode side of the fuel cell stack 2B to the atmosphere. The hydrogen outlet valve 11 is a control valve whose opening degree can be adjusted by a command from the electronic control unit 5 and controls off-gas released to the atmosphere.

  Further, the fuel cell system 1 includes a humidifier 12 in the middle of the oxidizing gas flow path 7 for supplying air from the compressor 4 to the fuel cell stack 2A. The humidifier 12 controls the humidity of the air flowing from the compressor 4 to the fuel cell stack 2 in accordance with a command from the electronic control unit 5.

  The fuel cell system 1 also includes an oxidant gas bypass passage 13 for bypassing the air flowing through the oxidant gas passage 7 to the fuel cell stack 2A. The upstream side of the oxidizing gas bypass channel 13 is connected to the oxidizing gas channel 7 that connects the humidifier 12 and the fuel cell stack 2A via the bypass valve 10B-O, and the downstream side is connected via the bypass valve 10A-O. The fuel cell stack 2A and the fuel cell stack 2B are connected to an oxidizing gas flow path 7 that connects the fuel cell stack 2A and the fuel cell stack 2B. The bypass valve 10 </ b> A-O and the bypass valve 10 </ b> B-O are electromagnetic three-way valves, and in accordance with a command from the electronic control unit 5, the air flowing through the oxidizing gas flow path 7 flows to the fuel cell stack 2 </ b> A side or the oxidizing gas bypass. Or flow to the flow path 13 side (the bypass path constituted by the bypass flow path and the bypass valve described above corresponds to the bypass means in the present invention).

  Further, the fuel cell system 1 includes an air outlet valve 14 in the middle of the oxidizing gas flow path 7 that discharges air off-gas from the cathode side of the fuel cell stack 2 to the atmosphere. The air outlet valve 14 is a control valve whose opening degree can be adjusted by a command from the electronic control unit 5, and controls the air off-gas released to the atmosphere.

  The electronic control unit 5 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an input / output interface, and the like, and includes a compressor 4, a humidifier 12, an air outlet valve 14, The hydrogen inlet valve 8, the hydrogen outlet valve 11, and the bypass valves 10A-H, 10B-H, 10A-O, and 10B-O are controlled. The electronic control unit 5 is electrically connected to a sensor (not shown) that detects the output voltage and output current of the fuel cell stack 2, and measures the output voltage and output current of the fuel cell stacks 2A and 2B. Further, the electronic control unit 5 detects the flow rate of hydrogen with a hydrogen flow rate sensor 15 provided in a passage between the hydrogen inlet valve 8 and the fuel cell stack 2A. Further, the electronic control unit 5 detects the flow rate and humidity of the air with the air flow rate sensor 16 and the humidity sensor 17 provided in the passage between the humidifier 12 and the fuel cell stack 2A.

  The electrical configuration of the fuel cell system 1 will be described. FIG. 2 is an electric circuit diagram of the fuel cell system 1. As shown in FIG. 2, the fuel cell system 1 is premised on being mounted on a vehicle that uses an electric motor as a drive source, and therefore supplies power to a motor 18 that drives the vehicle. The vehicle is driven by the drive wheels driven by the motor 18 and can move. The motor 18 is a so-called three-phase AC motor, and operates by receiving AC power from the inverter 19. The inverter 19 converts DC power supplied from the fuel cell stacks 2A and 2B, which are main power sources of the fuel cell system 1, and the battery 20 which is a secondary battery, into AC power and supplies the AC power to the motor 18. Between the fuel cell stacks 2A, 2B and the inverter 19, FC converters 21A, B which are DC-DC converters are electrically connected. Thereby, the voltage of the electric power output from the fuel cell stacks 2A and 2B is stepped up and down to an arbitrary voltage by the FC converters 21A and B and applied to the inverter 19. The FC converters 21A and 21B control the output voltage of the fuel cell stack 2A so that the outputs of the fuel cell stacks 2A and 2B operate in accordance with predetermined IV characteristics. Therefore, the step-up ratio on the secondary side (inverter side) with respect to the primary side (fuel cell stack side) is reduced so that the output voltage decreases if the output voltage of the fuel cell stacks 2A, B is higher than the predetermined IV characteristic. . On the other hand, if the output voltage of the fuel cell stacks 2A, 2B is lower than the predetermined IV characteristic, the step-up ratio on the secondary side with respect to the primary side is increased so that the output voltage increases.

  The FC converters 21A and 21B will be described in detail. The two FC converters 21A and 21B are DC-DC converters having the same performance, and are configured such that the FC converter 21A boosts the power of the fuel cell stack 2A, and the FC converter 21B boosts the power of the fuel cell stack 2B. ing. The output terminals of the FC converters 21A and 21B are electrically connected in parallel, and the electric power boosted by the respective converters is merged and then supplied to the inverter 19 and the battery boost converter 22.

  The battery 20 is a chargeable / dischargeable constant voltage power storage device, and is a boost type battery boost converter 22 between the battery 20 and the inverter 19 so as to be in parallel with the FC converter 21 with respect to the inverter 19. Are electrically connected. Thereby, the voltage of the power output from the battery 20 is boosted to an arbitrary voltage by the battery boost converter 22 and applied to the inverter 19. Hereinafter, a voltage applied to the inverter 19 (that is, a voltage of a circuit connecting the FC converters 21A and 21B and the inverter 19) is referred to as a system voltage. The battery boost converter 22 detects the voltage of power input to the motor 18 with a voltage sensor (not shown), and the voltage boost ratio so that the voltage of power input to the motor 18 becomes a voltage required by the motor 18. To control. Since the battery 20 is a constant voltage power source, the system voltage can be set to a predetermined control target value by adjusting the boost ratio of the battery boost converter 22.

In addition, when the electric load of the motor 18 increases, such as an increase in driving force required for the vehicle, and a force that pushes down the system voltage works, control is performed so that the system voltage becomes a predetermined control target value. Functions of FC converters 21A and 21B that control the output voltage of fuel cell stacks 2A and 2B to conform to a predetermined IV characteristic while the power supplied from battery 20 increases by the function of battery boost converter 22 As a result, the power supplied from the fuel cell stacks 2A and 2B increases. In addition, when the electric load of the motor 18 is decreased and a force that pushes up the system voltage is applied, such as a decrease in driving force required for the vehicle, the system voltage is controlled to become a predetermined control target value. Functions of FC converters 21A and 21B that control the output voltage of the fuel cell stacks 2A and 2B in accordance with a predetermined IV characteristic while the power supplied from the battery 20 is reduced by the functions of the battery boost converter 22. As a result, the power supplied from the fuel cell stacks 2A and 2B decreases. When the power consumption of the motor 18 is lower than the power supplied from the fuel cell stacks 2A and 2B, the power for boosting the system voltage is further increased.
The surplus power flows to the battery 20 side by the action of 2, and the battery 20 is charged. The electronic control unit 5 monitors the amounts of power passing through the FC converters 21A and 21B and the battery boost converter 22 that perform such voltage control, and power is supplied between the fuel cell stacks 2A and 2 and the battery 20. The buck-boost ratio of the FC converters 21A and 21B and the boost ratio of the battery boost converter 22 are appropriately adjusted so that the supply amount does not become unbalanced. For example, when the battery 20 is outputting a large amount of electric power even though there is a margin in the electric output of the fuel cell stacks 2A and 2B, the step-up ratio on the secondary side of the FC converters 21A and 21B with respect to the primary side is set. increase. As a result, the output power of the fuel cell stacks 2A and 2B increases, and the output power of the battery 20 decreases. Further, when the fuel cell stack 2B outputs a large amount of power despite the margin of electrical output of the fuel cell stack 2A, the boost ratio of the secondary side to the primary side of the FC converter 21A is increased, and the FC The step-up ratio on the secondary side with respect to the primary side of converter 21B is lowered. In this way, by appropriately adjusting the boost ratio and the step-up / step-down ratio of each FC converter 21A, B and battery boost converter 22, the distribution of the load of each power supply is adjusted.

  The FC converters 21A and 21B and the battery boost converter 22 are controlled by the electronic control unit 5 in the same manner as the compressor, humidifier, and valves. The electronic control unit 5 appropriately controls the power generation amount of the fuel cell stacks 2 </ b> A and 2 </ b> B and the charge / discharge amount from the battery 20 based on an accelerator pedal sensor that receives an acceleration request from the user, the rotational speed of the motor 18, and the like.

  Here, the movement of water in the fuel cell stacks 2A and 2B will be described in detail. FIG. 3 is a model diagram showing a movement state of water molecules in the membrane electrode assembly of each fuel cell stack when the fuel gas and the oxidizing gas are reacted. As shown in FIG. 3, water molecules contained in the fuel gas whose humidity has been adjusted move to the cathode electrode side along with protons that move through the electrolyte membrane. Therefore, the humidity of the fuel gas gradually decreases according to the flow direction of the fuel gas. For this reason, the humidity is more likely to decrease in the fuel cell stack 2A than in the fuel cell stack 2B. In addition, on the cathode electrode side where water accompanying the electrochemical reaction of hydrogen and oxygen is generated, the humidity of the oxidizing gas gradually increases according to the flow direction. For this reason, the humidity of the fuel cell stack 2B tends to be higher than that of the fuel cell stack 2A.

<Processing Flow of Embodiment>
Next, operation control of the fuel cell system 1 according to the present embodiment will be described. FIG. 4 is a control flow diagram of the fuel cell system 1. Hereinafter, the operation control of the fuel cell system 1 will be described with reference to the control flowchart shown in FIG.

  (Step S101: Power Generation Start Process) When the key switch of the fuel cell vehicle is turned on, the electronic control unit 5 controls the bypass valves 10A-H, 10B-H, 10A-O, and 10B-O to control the fuel cell. The gas flow path of the stack 2A is opened, and the fuel gas bypass flow path 9 and the oxidizing gas bypass flow path 13 are closed. The electronic control unit 5 opens the hydrogen inlet valve 8 and the hydrogen outlet valve 11 to supply hydrogen to the fuel cell stacks 2A and B, and opens the air outlet valve 14 to start the compressor 4 to start the fuel cell stack. Air containing oxygen is supplied to 2A and B. When the electronic control unit 5 starts supplying hydrogen and oxygen to the fuel cell stacks 2A and 2B, the hydrogen and oxygen undergo an electrochemical reaction in the membrane electrode assembly, and the power to the vehicle drive motor and auxiliary machinery Supply is started.

(Step S102: Parameter Acquisition) The electronic control unit 5 acquires the wet state of the electrolyte membrane of the membrane electrode assembly of the fuel cell stack 2A after starting the power generation by executing the process of step S101. When the electrolyte membrane is dry, the electrical resistance between the cathode electrode and the anode electrode of the membrane electrode assembly is higher than when the electrolyte membrane is wet. Therefore, the electronic control unit 5 measures the electric resistance of the fuel cell stack 2A with an electric resistance measuring device (not shown). The electrical resistance measuring instrument measures the electrical resistance by applying a high-frequency AC measurement current to the fuel cell stack 2A.

  (Step S103: Determination Process 1) When the electronic control unit 5 performs the process of step S102 and measures the electric resistance of the fuel cell stack 2A, whether or not the electrolyte membrane of the fuel cell stack 2A is dry based on the measurement result. Determine whether. The determination of the dryness of the electrolyte membrane is performed based on whether or not the electric resistance of the fuel cell stack 2A satisfies a predetermined threshold value. That is, if the electric resistance of the fuel cell stack 2A acquired by executing the process of step S102 is lower than a predetermined threshold value stored in advance in its own memory, the electronic control unit 5 performs normal operation until power generation is stopped. Continue (S105). On the other hand, if it is more than a predetermined threshold value, the recovery operation (S104) described later is executed.

  (Step S104: Recovery Operation) When the electronic control unit 5 determines to execute the recovery operation by the process of step S103, the electronic control unit 5 controls the bypass valves 10A-H, 10B-H, 10A-O, and 10B-O to provide fuel. The gas flow path of the battery stack 2A is blocked. Further, the electronic control unit 5 adjusts the opening of the hydrogen inlet valve 8 and the rotational speed of the compressor 4 to reduce the flow rate of hydrogen flowing through the fuel gas passage 6 and the flow rate of air flowing through the oxidizing gas passage 7. Half (corresponding to a predetermined ratio in the present invention). This is because the amount of reaction gas that needs to be supplied to two fuel cell stacks 2A, B having the same physique, in other words, two fuel cell stacks 2A, B having the same total reaction area is bypassed. This is because the fuel cell stack 2 </ b> A is isolated by switching the valve, and is halved. Therefore, the adjustment of the flow rate of the reaction gas is determined in proportion to the size of the reaction surface of the isolated fuel cell stack in the entire previous fuel cell stack. For example, one of the three stacks is adjusted. In case of isolation, the flow rate is set to 2/3. The flow rate of hydrogen and air may be adjusted not only by adjusting the opening degree of the hydrogen inlet valve 8 and the rotation speed of the compressor 4, but also by adjusting the opening degree of the hydrogen outlet valve 11 or the air outlet valve 14. Good.

  FIG. 5 shows the flow of hydrogen before the electronic control unit 5 switches the bypass valves 10A-H, 10B-H, 10A-O, and 10B-O to block the gas flow path of the fuel cell stack 2A in this step. FIG. 6 is a state diagram showing the air flow. As shown in FIG. 5, before the bypass valve is switched, the hydrogen supplied from the hydrogen storage tank 3 passes through the anode side of each membrane electrode assembly in the fuel cell stack 2B, and then in the fuel cell stack 2A. It passes through the anode side of each membrane electrode assembly. Also, as shown in FIG. 6, before switching the bypass valve, the air supplied from the compressor 4 passes through the cathode electrode side of each membrane electrode assembly in the fuel cell stack 2A, and then in the fuel cell stack 2B. It passes through the cathode electrode side of each membrane electrode assembly.

  FIG. 7 is a state diagram showing the flow of hydrogen after the electronic control unit 5 switches the bypass valve and shuts off the gas flow path of the fuel cell stack 2A in this step, and FIG. 8 also shows the flow of air. It is a state diagram. As shown in FIG. 7, after switching the bypass valve, the hydrogen supplied from the hydrogen storage tank 3 passes through the anode side of each membrane electrode assembly in the fuel cell stack 2B, and then the fuel gas bypass channel 9 And bypass the fuel cell stack 2A. Also, as shown in FIG. 8, after switching the bypass valve, the air supplied from the compressor 4 passes through the cathode electrode side of each membrane electrode assembly in the fuel cell stack 2A and then the oxidizing gas bypass flow path 13 And bypass the fuel cell stack 2B.

FIG. 9 is a diagram comparing the state before and after switching of the bypass valve with respect to the state of the flow of hydrogen flowing on the anode side of the membrane electrode assembly and the flow of air flowing on the cathode side. By switching the bypass valve, the flow of hydrogen flowing on the surface on the anode side of the membrane electrode assembly of the fuel cell stack 2A disappears, and the flow of air flowing on the surface on the cathode side disappears. As a result, the following phenomenon occurs. FIG. 10 is a model diagram showing the movement state of water molecules in the membrane electrode assembly of each fuel cell stack after switching the bypass valve to isolate the fuel cell stack 2A. The water molecules that have moved and gathered to the cathode side accompanying the proton moving in the electrolyte membrane move to the dry anode side as the proton movement stops due to the stop of power generation in the fuel cell stack 2A. start. As a result, the anode side of the electrolyte membrane of the fuel cell stack 2A, which has been dried due to the uneven distribution of water molecules on the cathode side, is moistened and becomes wet enough to generate power.

  The electronic control unit 5 controls the FC converters 21A and 21B as follows simultaneously with the separation of the fuel cell stack 2A by the control of the bypass valve. That is, the electronic control unit 5 stops the FC converter 21A simultaneously with the isolation of the fuel cell stack 2A by the control of the bypass valve, and interrupts the electrical connection between the fuel cell stack 2A and the load (motor 18 or the like). This is because the movement of protons in the electrolyte membrane of the fuel cell stack 2A is quickly stopped, and water molecules that are unevenly distributed on the cathode side are quickly moved to the anode side. Further, the electronic control unit 5 changes the step-up / step-down ratio of the FC converter 21B simultaneously with the switching of the bypass valve so that the load of the battery 20 does not become excessive due to the stop of the FC converter 21A, and the fuel cell stack 2B and the battery 20 And adjust the load distribution. For example, when the load distribution of the fuel cell stack 2A, the fuel cell stack 2B, and the battery 20 is 4 to 4 to 3, and the fuel cell stack 2A is stopped, the load distribution is 0 to 5.7 to 4. Therefore, the boost ratio of the secondary side with respect to the primary side of the FC converter 21B is increased, and the ratio of the load of the fuel cell stack 2B to the battery 20 is increased.

  The electronic control unit 5 executes the processing after step S102 again after switching the bypass valve. When the electrolyte membrane of the fuel cell stack 2A becomes wet enough to resume power generation, the electric resistance of the fuel cell stack 2A becomes equal to or greater than a predetermined threshold value. Therefore, in the determination process of step S103, the process of step S105 is performed. Execution of processing is selected.

  (Step S105: Determination Process 2) The electronic control unit 5 determines whether or not to continue power generation. That is, if the key switch of the fuel cell vehicle remains on, the electronic control unit 5 executes the above-described processing after step S102 again. On the other hand, when the key switch of the fuel cell vehicle is turned off, the electronic control unit 5 stops the power generation of the fuel cell system 1 by executing the process of the next step S106.

  (Step S106: Power Generation Stop Processing) When the stop of power generation in the fuel cell system 1 is determined by the processing in step S105 described above, the electronic control unit 5 stops the FC converters 21A and B and stops the fuel cell stacks 2A and B. Disconnect the electrical load connected to the. The electronic control unit 5 closes the hydrogen inlet valve 8 and the hydrogen outlet valve 11 to stop the supply of hydrogen to the fuel cell stack 2, and stops the compressor 4 and closes the air outlet valve 14 to close the fuel cell. The supply of oxygen to the stack 2 is stopped. Thereby, an electrochemical reaction stops and the stop process of the fuel cell system 1 is completed.

<Effect of embodiment>
As described above, according to the fuel cell system according to the above embodiment, when the electrolyte membrane of some fuel cell stacks is dried and power generation failure occurs, the supply of gas to the fuel cell stack is interrupted. Since removal of water is suppressed, drying of the electrolyte membrane of another fuel cell stack is suppressed. In addition, since the gas does not pass through the fuel cell stack where the power generation failure has occurred, the temperature of the other fuel cell stack can be maintained appropriately and a good power generation state can be maintained. In this way, the flow of gas in the fuel cell stack in which power generation failure has occurred is cut off, so that the power generation state of other fuel cell stacks is kept normal, and a decrease in the generated power of the entire fuel cell system is suppressed. .

<Modification>
The fuel cell system according to the above embodiment may be modified as follows. FIG. 11 is an enlarged view of a main part of the fuel cell system according to the first modification. As shown in FIG. 11, the fuel cell system according to the above embodiment may include a plurality of fuel cell stacks having no bypass path. In this case, all of the plurality of fuel cell stacks that do not have a bypass path correspond to the first fuel cell stacking portion referred to in the present invention.

  FIG. 12 is an enlarged view of a main part of the fuel cell system according to the second modification. As shown in FIG. 12, the fuel cell system according to the above embodiment may include a plurality of fuel cell stacks having bypass paths. In this case, all of the plurality of fuel cell stacks having the bypass path correspond to the second fuel cell stacking portion referred to in the present invention.

  FIG. 13 is an enlarged view of a main part of the fuel cell system according to the third modification. As shown in FIG. 13, the fuel cell system according to the embodiment may include a plurality of fuel cell stacks having mutually independent bypass paths. Then, when the electrolyte membrane of any one of the plurality of fuel cell stacks having bypass paths independent from each other is dried, the fuel cell stack may be bypassed. In this case, each of the plurality of fuel cell stacks having bypass paths independent from each other corresponds to the second fuel cell stack portion in the present invention.

The block diagram of a fuel cell system. The electric circuit diagram of a fuel cell system. The model figure which shows the movement state of a water molecule. The control flow figure of a fuel cell system. The state diagram which shows the flow of hydrogen before interruption | blocking. The state figure which shows the flow of the air before interruption | blocking. The state diagram which shows the flow of hydrogen after interruption | blocking. The state figure which shows the flow of the air after interruption | blocking. The figure which compared the flow of the gas of a membrane electrode assembly. The model figure which shows the movement state of the water molecule after isolation. The block diagram of the 1st modification of a fuel cell system. The block diagram of the 2nd modification of a fuel cell system. The block diagram of the 3rd modification of a fuel cell system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2A, B ... Fuel cell stack 3 ... Hydrogen storage tank 4 ... Compressor 5 ... Electronic control apparatus

Claims (4)

A fuel cell system that generates electricity by an electrochemical reaction between a fuel gas and an oxidizing gas,
A first fuel cell stacking unit and a second fuel cell stacking unit in which membrane electrode assemblies that are joined so as to sandwich an electrolyte membrane between catalyst electrode membranes are stacked;
A fuel gas flow path for flowing the fuel gas through the first fuel cell stack and the second fuel cell stack in the order of the first fuel cell stack and the second fuel cell stack; A fuel gas flow path that passes through the catalyst electrode membrane on the fuel electrode side of the membrane electrode assembly of each fuel cell stack,
An oxidizing gas flow path for flowing the oxidizing gas through the second fuel cell stack and the first fuel cell stack in the order of the second fuel cell stack and the first fuel cell stack. An oxidizing gas flow path that passes through the catalyst electrode membrane on the oxygen electrode side of the membrane electrode assembly of each fuel cell stack,
It is determined that the electrolyte membrane of the membrane electrode assembly of the second fuel cell stack is dry with the fuel gas flowing through the fuel gas channel and the oxidizing gas flowing through the oxidizing gas channel. When the oxidizing gas flowing through the fuel gas passage fuel gas and oxidizing gas flow path through the by Rukoto bypass the said second fuel cell stack unit, in association with the movement of protons in the electrolyte membrane Bypass means for returning the accompanying water that has moved to the cathode side to the anode side and recovering the dried portion to a wet state ,
Fuel cell system. When the bypass means bypasses the second fuel cell stack, the second fuel cell occupies the area of the entire membrane electrode assembly of the first fuel cell stack and the second fuel cell stack Flow rate control means for reducing the flow rate of the fuel gas flowing through the fuel gas flow channel and the flow rate of the oxidizing gas flowing through the oxidizing gas flow channel by a predetermined ratio that is a ratio of the area of the membrane electrode assembly of the stacked portion. In addition,
The fuel cell system according to claim 1. When the electrolyte membrane of the membrane electrode assembly of the second fuel cell stack is wet with the bypass means bypassing the second fuel cell stack, the fuel in the second fuel cell stack is Flowing fuel gas and oxidizing gas through the gas channel and oxidizing gas channel,
The fuel cell system according to claim 1 or 2. The bypass means detects dryness of the electrolyte membrane of the membrane electrode assembly based on the conductivity of the membrane electrode assembly of the second fuel cell stack.
The fuel cell system according to any one of claims 1 to 3.

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